Standard practice in envelope tracking transmit systems is to supply a power amplifier (PA) with a modulated supply voltage that is proportional to the instantaneous amplitude of an RF waveform. A related art technique modulates a supply voltage to be exactly proportional to the instantaneous amplitude of an RF waveform being amplified by the PA. Moreover, the supply voltage is adjusted to achieve constant gain at all power levels. As such, the related art technique provides improved transmitter linearity by eliminating AM/AM distortion. However, under certain conditions a high supply voltage may be required to maintain constant gain at low power levels. A resulting supply voltage waveform has significantly more high frequency content, which places increased demands on a modulator and degrades system efficiency. What is needed is a new technique for retaining the benefit of iso-gain envelope tracking without increased modulator requirements that results in a loss of system efficiency. In particular, a new technique for defining a quasi iso-gain supply voltage function retains the improved linearity benefit of an iso-gain envelope tracking system without incurring a loss in efficiency.